In the conventional art, multilayered packaging materials with double or more layers have been proposed. They are composed of polyamide resin and polyolefins such as polyethylene or other highly gas-impermeable resins such as ethylene-vinyl alcohol copolymer, polyvinylidene chloride and polyacrylonitrile. The multilayered packaging materials of this kind have excellent combined characteristics of piercing resistance, thermal resistance, low-temperature resistance and gas impermeability which are inherent in the polyamide resin, moisture impermeability and heat-sealable property which are inherent in the polyolefin resin and excellent gas impermeability which is inherent in ethylene-vinyl alcohol copolymer. Thus they have been widely used for food packaging, especially as bags for meat, pickles, cakes, sauces, soups and the like.
The multilayered packaging materials made of the above combination are produced by methods of coextrusion, dry lamination or the like. As for the kinds of the packaging materials, there are non-oriented materials which are obtained by co-extrusion and wholly or partially oriented multilayered packaging materials which are made by biaxially orienting a single resin such as polyamide, polypropylene, ethylene-vinyl alcohol copolymer or polyethylene-terephthalate and then joining the oriented resins together by using a method of dry lamination or extrusion lamination.
In these conventional multilayered packaging materials, non-oriented type is characterized by the excellent piercing resistance which is inherent in the polyamide resin. However, the material is hardly torn, so that it poses a problem, for example, in the difficulty to be opened in the case of the widely used packaging bags.
As for the packaging materials obtained by laminating biaxially oriented resins, they have good tearability, however, the direction of tearing cannot be settled. Furthermore, when the packaging bags are made by laminating with a sealant resin layer, their tearability is impaired and the easily opening property is not good.
As a result of investigations carried out by the inventors to solve the above disadvantages in the conventional arts, the present invention has been accomplished.